Aluminum has a relatively low density and high strength. Accordingly, aluminum by itself or alloyed with other metals is useful in many applications as it permits light weight constructions. For example, this feature of aluminum makes aluminum desirable for both beverage cans and aluminum alloy wheels. With the increasing use of aluminum in these contexts, and the resultant increase in demand for aluminum, it is also increasingly important that constructions made from aluminum be efficiently recycled.
Prior art technologies have been devised to recycle aluminum. For example, U.S. Pat. No. 5,133,505 discloses a method and apparatus for separating aluminum alloys from other materials. This invention relies on magnetic separation and subsequent shredding. However, for a number of reasons, the process and apparatus taught by this patent are not ideal for recycling aluminum alloy wheels. That is, the prior art method and apparatus are neither suitable for single source aluminum recycling material such as aluminum alloy wheels. Further, these prior art technologies do not teach an effective way of dealing with contaminates that may be on the surface of aluminum products such as aluminum alloy wheels.
Aluminum car wheels are made of high purity aluminum alloy—often from Aluminum Association alloy number A356.2. In addition to the high purity aluminum alloy, car wheels may also comprise the following materials: paint, clearcoat, chrome plating, lead weights, brass, rubber, brass fittings, stainless steel or iron inserts. If an alloy wheel made from alloy number A356.2 is melted while contaminated with too much of any of these metals, then the composition of the melt will vary from the specification required of alloy A356.2 and will not be suitable for use in casting new alloy wheels made from alloy A356.2. As a result, aluminum alloy wheels are often recycled to produce less valuable products. For example, aluminum alloy wheels are often re-melted and used in the production of a secondary alloy, namely alloy A356.1, or as an iron diluter for the production of various lower purity aluminum alloys.
The value of alloy A356.1 or iron diluters is less than that of alloy A356.2. Therefore, when aluminum alloy wheels are recycled in this manner, much of their latent value is lost as the resulting recycled material is less valuable than the high purity aluminum alloy A356.2 from which the aluminum wheels were originally made.
The paint and clearcoat present on the wheels are also of concern when alloy wheels are remelted for recycling or if the wheels are first heated to remove these contaminants as these contaminants may release toxic fumes during re-melting. Therefore additional environmental equipment, such as bag houses, are required which increases the cost of recycling.